feat: expanded tag color system

[CyanVoxel]

Summary

This PR adds a new expanded tag color system and lays the foundation for user-created tag colors. Instead of colors being stored as strings or enums, tag colors are now represented by a namespace and associated slug ID. Namespaces must be unique, and slugs only need to be unique within their respective namespace. This system has the following advantages:

1. Built-in TagStudio tag colors can be completely separated from user colors
2. This system allows for colors to be shared between libraries, unlike a traditional incrementing ID system
3. Built-in TagStudio tag colors can be further organized into different reserved namespaces

In addition, tag colors now have "primary" and optional "secondary" colors. Primary colors are used as the default base color of the tag, with text and border colors being derived from this. Secondary colors are optional and replace the border and text colors with a specific value. These secondary colors can be seen with the new "Neon" tag color group. Several other new tag colors have been added, and some have either been renamed or consolidated. This is most notable with the changes made to "Blue Violet", "Violet", and "Purple" which have been consolidated into "Indigo" and "Purple", with JSON "Blue Violet" now mapping to the new "Navy" color.

Finally, a new color selection modal has been added which replaces the old color name combobox. This provides a much cleaner visual approach to selecting colors, which will also serve as the home for user-created colors.

This framework should mean that the only thing left for user-created colors would be a proper UI for creating and editing these tag color groups. Furthermore, it wouldn't take too much work on top of this to enable the importing and exporting of tag color packs, once a sharable format for those is decided upon.

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Closes #623, Progress towards #264